Process for converting metals and the like



. 9, 1941. R. MAIER PROCESS FOR CONVERTING METALS AND THE LIKE 3Sheets-Sheet 1 Original Filed June 7, 1937 INVENTOR ATTORNEY RUDQLF MA IER Original Filed June 7, 1937, 3 Sheets-Sheet .2

INVENTOR R. MAIER Dec. 9,1941.

PROCESS FOR CONVERTING METALS AND THE LIKE Original Filed June 7, 1937 3Sheets-Sheet 3 INVENTOR @UDOLF NIH/5 Q TTORNEY Patented Dec. 9, 19412,265,180 raoosss FOR CONVERTING METALS AND THE LIKE Rudolf Maier,Stuttgart, Germany, asslgnor to Elektro-Metallurgische ApparatebauAktlengesellschait, Zurich, Switzerland, a corporation of SwitzerlandOriginal application June '1, 1937, Serial No.

146,748. Divided and this application August. 24, 1939, Serial No.291,689

6 Claims.

the process of the present invention can be adapted to a great varietyof purposes.

The present invention provides a process in which substances to betreated .are introduced into a furnace or crucible in small amounts atany one instant. The crucible is provided with asubstantially planesurface onto which the substances are fed in small amounts and preventedfrom forming greater coherent complexes such as heaps or pools of thesubstances to be treated. Preferably, the substantially plane surface issubjected directly to the heat of the furnace or crucible and providesan unobstructed surface on which the particles of the substance to betreated are free to move.-

It is an object of the present invention to provide a process for thevaporization of metals, metal alloys, metal compounds and the like inwhich the individual particles or grains of the substance to be treatedare separately subjected to the action of heat.

It is another object of the present invention to provide a process inwhich only such amounts of substances to be treated are introduced intothe furnace or crucible as are substantially equivalent to the amountsvaporized.

It is a further object of the present invention to provide a process inwhich such high temperatures are employed that due to spontaneousvaporization, the individual particles or small accumulations of thesubstances to be treated are completely surrounded by vapor originatingfrom the substances.

The present invention also contemplates a. process in which small,discrete particles. of a substance to be treated are subjected totemperatures substantially above the-boiling point of the substances. 4

The present invention likewise contemplates a process for vaporizingmetals, metal alloys, metal compounds and the like in which temperaturesabove those at which the Leidenfrost phenomena becomes effective areemployed.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the drawings, in which Fig. 1 is adiagrammatic sectionalview of a crucible embodying the principles ofthepresent invention;

Fig. 2 is a longitudinal vertical section through a crucible embodyingthe principles of the present invention;

Fig. 3 is a modified construction of a furnace according to theinvention;

Fig. 4 shows a section through another modifled furnace accordingto theinvention;

Fig. 5 is a sectional view of a further modification of a crucibleaccording to the invention; and

- Fig. 6 is a horizontal section through the furnace shown in Fig. 5.

As shown diagrammatically in Fig. 1, the

furnace or crucible I, consisting of sheet iron,'. has a bottom 2 and isprovided at the upper endwith an outlet socket 3 which is connected witha chamber 4 for collecting the developed gases or vapors. -The bottom 2of the furnace l is covered by a plate 5 of graphite or the like, theupper surface of which is substantially even, or at least so constructedas to prevent a greater accumulation or collection of particles or dropsof the material or substances to be treated. A tube 6 extends throughthe walls of the crucible or furnace I and this tube is connected to astorage container or reservoir 1 for the material or substance to betreated. The tube- 6 is proconnected to the electrodes 9 by a circuit l2in which an ammeter I3 is arranged.

The container or reservoir 1 is filled withgranular material, if suchmaterial is to be treated, or the container is filled with liquid metal.By opening the shutoff valve 8 the material is fed into the furnace l invery small amounts at a time, preferably in form of individual grains ordrops 14. In the very moment the drop it or the grain, introduced by wayof the tube 6, reaches the plate 5 of the highly heated crucible I, thisgrain or drop is completely surrounded by the vapor l5 developed in thecrucible in such a manner, that said grain or drop in fact is somewhatlifted from the upper surface of the plate 5. Due to the fact that thedrop I is surrounded by the vapor t5. the well known Leidenfrost'phenomenon is obtained. The drop M then is quickly moved to and fro inthe furnace .or crucible I. The developed vapors finally pass throughthe socket 3 of the furnace or crucible I into the chamber I from wherethey are conducted to any desired place of use. If granular material isto be treated, the same effect is obtained, if the material is fed intothe crucible in such a manner as to reach the surface of the plate 5 inthe form of individual grains.

Fig. 2 shows a construction of a furnace or crucible for practicallycarrying out the new process. In this construction, the casing l8.consisting preferably of sheet iron, is lined with a refractory materialI? in whichthe crucible I3 is embedded. The furnace or crucible i3 isclosed at the upper end by a conical portion l9. Into the crucible 18extend three tubes 28 one of which only is shown in the drawings for thesake of clearness'. Each of the tubes 20 is fixed in position by meansof a bracket 2i and serves the purpose of holding an electrode 22 whichextends through the conical portion I9 into the interior of t e furnaceor crucible l8. In the drawing one of the elect odes 22 is shown in fulllines, while the second one is shown in-dotted lines only and the thirdone is notshown at all. Each of these electrodes 22 is, by insulations23, electrically insulated with regard to the tube 20, the bracket 2|and the casing l6. From the conical portion l9 a tube 24 leadsto a tube25 which may be connected to a place of use for the gases or vaporsdeveloped in the interior of the crucible IB. Extending through thecasing-wall IS, the refractory lining i1 and the conical portion IQ ofthe crucible I8 is a tube 28 the upper'end of which carries atransparent plate 21 allowing observation of the interior of thecrucible during operation. Exteriorly of the casing IS a tube 28 isprovided which opens into the tube 26 and is connected to the storagetank or container 29 for the material to be treated. The tube 28 isprovided with a control valve 3%). Into the bottom of the crucible It atube Si is inserted which slightly extends over the upper surface of aplate 32 consisting of graphite or the like. The tube 3! is open at theupper end and its lower end is connected to a funnel-like opening 33 ofa tube 34 extending through a bushing 35 and the bottom 36 of the casingl5 into a tank 31 fixed to a socket 38 of the bottom 36. A dischargetube 39 leads from the tank 31. Journaled in brackets 40 fixed to thebottom 36 of the casing l8 are wheels 4! allowing movement of the entirefurnace or crucible fromone place to another for the purpose ofconnecting same as desired to One or the other device in which thevapors of the metals, metal alloys, etc., produced in the crucible maybe subjected to the desired treatments.

The operation of this furnace or crucible is fundamentally the same asthat described in connection with Fig. 1. Should for any reason toogreat an amount of the material to be treated be fed at a time into thefurnace or crucible l8 the to the crucible may be controlled in anysuitable manner.

If instead of granular material, liquid metal or metal alloys, forinstance iron, are to be vaporized, the iron is fed into the crucible i8preferably in form of a wire. The storage tank 29 and the valve 39controlling the feed of the granular or liquid material or substance tobe treated are then replaced by other devices which need not be shown ordescribed, as they are well known to men skilled in the art.

In some cases the devices controlling the feed of the substances to bevaporized may be so constructed, that they are automatically adjusted inaccordance with the proceeding of the vaporization process. This controlmay for instance be effected by means of relays operating in dependenceon the temperature prevailing in the crucible, the electrical load, thelevel of the substance or other factors adapted to be indicated bymeasuring instruments.

The tube 35 may consist of graphite and is preferably heated by electriccurrent to a suitable temperature. The tank 31 is also preferablyheated. The means required for this purpose are not shown in thedrawings as they do not form part of the present invention.

Asmentioned already above, the upper surface of the plate 32 ispreferably even. This plate, preferably consisting of graphite, isarranged in a horizontal plane and its upper surface may have smalldepressions which allow a limitation of individual drops of the liquidwhich, however, are so chosen, that heapor pond-like accumulations orcollections of a plurality of drops in one and the same depression areimpossible.

"The electrodes 22 are connected in star connection with the coils of 'athree-phase current transformer 62. The star-point is connected to thecasing Q6 of the furnace or crucible l8 and grounded. The primarycurrent is supplied from a three-phase current line and its tension iscontrolled by control means well known in the art.

The electrodes may also be connected in another manner or be suppliedwith two-phase cur rent or direct current. If desired, one electrodeonly may be provided in which case the crucible 58 or the plate 32serves as counter-electrode.

With certain of these connections rectifier effects may occur and,therefore, it may be preferable to connect an instrument, indicating andmeasuring direct current, in the circuit leading to the crucible orfurnace l8.

If copper is to be vaporized in the apparatus according to theinvention, the operation is as follows if the transformer. has acapacity of 200 kilowatts.

When by switching on the current and forming the electric arc thefurnace or crucible I8 is heated suficiently high, liquid copper is fedinto the crucible from the storage tank or reservoir 23 in an amountsufficient to cover the bottom of the crucible or the upper surface ofthe graphite plate 32, if such a plate is used, with. a very thin layerof liquid copper. The electrical load is then increased so far, that thecopper vaporizes which, as shown by experiments, takes place slowly onlyas long as a coherent supply of liquid copper is present in thecrucible. As soon as the liquid copper fed into the crucible is aboutexhausted and thereby the bottom of the crucible or the upper surface ofthe plate 32 begins to be free of copper to be treated, a surprisingincrease of the rate of vaporization results. Simultaneously the wellknown Leidenfrost phenomenon that vaporized at a time in the furnace.

appears, that is to say,the greater and smaller drops still present areso quickly vaporized upon the plate 82, that they are somewhat lifted bythe vapor from the plate. The individual drops are completely envelopedby vapor and are quickly moved to and fro in the crucible and finallysplashed. Due to the extremely powerful heat radiation in the interiorof the crucible, the drops are very quickly solved and vaporized, andthe vapor is heated to a temperature far above the boiling point. Thisis still favored by the fact, that the vapors developed are compelled toflow through the electric arc.

As soon as the Leidenfrost phenomenon comes.

to action and the vaporization starts, care is to be taken that freshliquid copper is supplied to the crucible or furnace in an amount equalto If these conditions are maintained, the most favorable relations forthe vaporization are obtained. The valve 36 controlling the feed of thematerial is of 1 course, opened sufficiently wide for this'purpose.

The amount of material required to obtain correct operating conditionsmay be calculated from the copper to a temperature of 2100"" C., 42 calories are required for the melting, 1100 calories for vaporization andabout 150 calories for superheating to 500 C.

Theoretically the vaporization space remains in heat equilibrium if 146200/1536 equal to 93.5 kg. of copper are supplied per hour in an uniformstream of flow. In practice, the amount fed is somewhat below the weightgiven above.

The control of the amount of material fed into the furnace offers nodifllculties, because the process automatically is stabilized to acertain degree, if the transformer operates somewhat elastically. If toomuch copper is introduced, the electric arc consumes more energy and,therefore, a greater amount of copper is vaporized. Porosities and boresin the plate 32, or generally a sponge-like structure of the platefacilitate the stability and controllability of the operation.

The fact that the Leidenfrost phenomenon comes to action simultaneouslywith a strong increase of the rate of vaporization is probably due tothe fact, that the rests of the molten metal are thermically isolatedfrom the bottom of the furnace or crucible by the metal vaporsurrounding or embedding them. Consequently the heat supply byconvection from the bottom decreases, but 7 simultaneously also thewithdrawal of heat, because the vapors are not as good a heat conductoras the liquid. Compared with their mass the isolated drops have a greatsurface and absorb great amounts of radiating heat, the intensity ofwhich in the hollow space of the crucible increases with the biquadrateof the absolute temperature, whereas the withdrawal of heat byconvection increases slower with the temperature. It is immaterialwhether or not the surprising increase in the rate of vaporization iscaused by the Leidenfrost phenomenon. In any case theoccurrence of theLeidenfrost phenomenon, is a reliable criterion of the fact, that thecrucible operates under correct conditions to obtain an intensivevaporization of the metal.

Other metals and metal alloys may also be stance to be vaporized only isfed into the vaporization space always as is vaporized in the same, andthat the temperature of the space is maintained above that at which theLeidenfrost phenomenon begins to become effective.

The quantities or amounts of the substances to be treated and to be fedmay be calculated from the thermal constants of the respective substanceand the arc load. If the figures required for the calculation areonlyapproximately known, they may be estimated and corrected duringoperation.

The process according to the invention may also be used for treatingother substances, for instance metal compounds, as oxides, sulphides a.s. 0., even if these substances are directly converted from the solidstate into the vapor state. For instance, ores of nickel, copper, zincand other metals have often been decomposed according to the new processinto their constituents by converting ores, as they come from the pit,by well known means into a fine dry powder which by drizzlingit througha supply pipe is slowly and preferably uniformly fed into the interiorof the furnace. Each individual ore particle then vaporizes practicallyfor itself and a superheated vapor mixture results from the constituentsof the ore. This vapor mixture is then, preferably outside the furnacedecomposed or separated into its constituents and cooled, the individualconstituents being obtained in separate vessels or tanks as a finepowder. As is well known, many of these powders have the property that,at the temperatures coming into consideration, they do not fuse butsublimate. In treating such substances a variety of the Leidenfrostphenomenon occurs with solid particles. These substances similarlybehave as drops and vaporize so quickly, that they are lifted from theirsupport by the vapor layer surrounding them. These particles, however,are not irregularly moved to and fro upon their support as is the casewith liquids. A temperature may, however, be found beyond which the rateof the vaporization of -late upon the surface of the crucible and toreduce the temperature of these points.

It may be of advantage to superheat the metal vapors, leaving thevaporization space, by means ofadditional heating surfaces, for instanceby electrically heated tubes, plates or the like of graphite.

If necessary, all parts of the device for carry ing out the newprocesswhich must be heated to high temperatures are protected againstburning by introducing neutral gases, for instance, nitrogen, as long asthe gas produced in the furnace is not able to warrant this protection.

The process of vaporization is carried out in the device described atabout atmospheric pressure. It may, however, also be of advantage tocarry out the process under higher pressure and in some cases also underlower pressure. For this purpose the furnace or crucible and the spacesconnected thereto are sufficiently sealedagainst the atmosphere and therequired vacuum and pressure respectively is obtained by means ofsuction pumps and pressure pumps respectively. The various devices andoperations required for to very high temperatures.

skilled in the art. so that a more detailed description of same appearsto be unnecessary here.

The process according to the invention shown in Fig. 3 consists of acrucible 43 of graphite or the like which is heated by Joule heat. Forthis purpose the lower portion of the crucible 43 is embedded in atrough 44 consisting of conductive material, which trough is filled withsmall coal 45. From the conical upperportion 46 of the crucible extendsupwardly a tube 41 of conducting material which is connected to anothertube 48. The upper end of the tube 4! is surrounded by a pipe clip 49 bymeans of which the current of a transformer 50 is conducted to the tube41 forming th upper part of the crucible 43, so that the latter isintensively heated. A tube-| connected to a storage tank .or reservoir52 and provided with a control valve 53 is connected to the upper part46 of the crucible 43.

' The operation of this device is similar to that described inconnection with the construction the closed end of the tube 54 and to astorage tank or reservoir 58 for the material to be treated. With thisconstruction also the temperature is raised to such a degree, that thematerial, fed

into the device, splashes upon the hot wall of the tube '54, isconverted into vapor and further superheated on the way to the dischargeend of the tube 54 which may be connected to a place of. use of thevapors. Due to the inclined arrangementof the tube 54 all drops notimmediately vaporized roll back again and again until they arecompletely vaporized.

According to Figs. 5 and 6 the crucible or furnac consists of a hollowring 59 of graphite or the like which surrounds a shank 60 of a transformer core 6| carrying the coil 62. The ring 69 forms the secondarycoil and is, duringoperation of the transformer, traversed by heavycurrents, with the result that the ring 59 is heated A tube 63 providedwith a control valve 64 is connected to the rin 59 and to a storage tankor reservoir 65 for the material to be treated. The vapor. produced'inthe ring 59 flows through the tube 66 and is led to a suitable'place ofuse.

It has been found that in carrying out the' process of the presentinvention rectifier effects may occur. By means of a direct currentindicator connected to the circuit supplying current to the furnace orcrucible, these effects may be observed and utilized for controlpurposes.

The metal powder obtained by the new process is characterized by thefact, that all of the primary particles of the powder are of a size nearthe limit of microscopical visibleness and that the secondary particlesare extremely loose flocks also of microscopical smallness.

Exmeuss Calories Supposed furnace efficiency: 200 kw.

860 calorie 172,000 15% loss of heat due to transfer to surroundingatmosphere 25,800

Available heat value in the furnace space 146,200

To maintain equilibrium of heat the process may be carried out accordingto the following examples:

heat value per kg. of copper 1,563 calories equal to 93.5 kg. per houras highest admissible quantity of the supply.

2. Zinc Calories 0-420 42 420-918" 60 Latent heat of fusion 28vaporization heat 436 Supposed superheating heat Total 666 Highestadmissible quantity of supply calculated as above: 146,200 divided by666=2l9.5 kg.

Highest admissible quantity of supply calculated as above: 146,200divided by 2142.4==68.2 kg. per hour.

5. Lead Calories 0-230 8.74 230-1560 66.50 Latent heat of fusion 5.86vaporization heat 220.00 .Supposed superheating heat 30.00

Total 331.10

Highest admissible quantity of supply calculated as above: 146,200divided by 331.10=441.5 kg. per hour.

6. Zinc Oxide Calories 0-1850 196 Latent heat of fusion (does not fusebut sublimates) Vaporization heat (sublimation heat) 959 Supposedsuperheating heat 100 Total s 1,255

Highest admissible quantity of supply cal-- Highest admissible quantityof supply cal-.

culated as above: 146,200 divided by 894::1655

kg. per hour.

8. Zinc sulphide, zinc blende Calories Supposed sublimation heat 950Supposecl'superheating heat 90 Total 1,256

Highest admissible quantity of supply calculated as above: 146,200divided by 1256:116 kg. per hour. 4

9. Lead sulphide, gqlena Calories 0 1344 80.6 Supposed meltingandvaporization heat 250 Supposed superheating heat 30 Total 360.6

Highest admissible quantity of supply calcu-' lated as above: 146,200divided by 360.6=405.4 kg. per hour.

2. A process for vaporizing metals, metal alloys, metal compounds andthe like which comprises introducing a metal, metal alloy, metalcorrpound and the like into a closed reaction chamber onto a heatradiating and vaporizing surface heated to a temperature above thevaporizing temperature of said. metal and the like, heating said metaland the like as substantially discrete particles on said vaporizingsurface until said metal and the like have been converted into the vaporstate, withdrawing said vapors from said chamber substantially withoutcondensation and condensing said vapors.

3. A process for vaporizing and gasifying metals, metal alloys, metalcompounds and the like to produce finely divided material whichcomprises establishing a pool of molten metal to be vaporized,introducing said molten metal and the like onto a highly heated, heatradiating vaporizing surface within a vapor tight chamand vaporizingsurface therein in such quantity as to form a thin liquid film on saidvaporizing surface, heating said vaporizing surface until the majorportion of said thin-liquid film has been vaporized, introducing furtheramounts of In practice the quantity of supply must, of'

course somewhat be kept below the theoretically calculated quantities.

The present application is a division of my oopending application,Serial No. 146,748, now Patent #2307346, relating to an Apparatussuitable for vaporizing metals.

Although the present invention has been described in conjunction withcertain preferred embodiments, variations and modifications may be madetherein as those skilled in the art will readily understand. Suchvariations and modifica- 'tions are to be considered within the purviewof a drop as soon as it is fed onto the refractorysaid metal into saidchamber and onto said radiating surface at a rate substantiallyequivalent to the rate at which said material is vaporized, withdrawingvapors from said chamber substantially without condensation andcondensing said vapors.

5. A process for vaporizing and gasifying m,

terials including metals, metal alloys, metal compounds and the like toproduce finely divided material which comprises feeding a material to beI temperature of said material while. said material surface, wherebysubstantially the entire surface of the material to be vaporized issubjected to heat by radiation and said material is thereby convertedinto the vapor state, in which condition said material is dischargedfrom the vaporizatlon chamber and condensed.

is in the form of discrete particles to vaporize said material,withdrawing said vapors substantially without condensation andcondensing said highly-heated vaporizing surface, heating said materialin the form of discrete particles to a temperature substantially abovethe vaporizing temperature of said material and to a. temperature atwhich the Leidenfrost phenomenon be"-' comes effective to vaporize saidmaterial, with-' drawing said vapors and condensing said vapors.

RUDOLF m

